1. Field of the Invention
This invention relates to an ink fountain apparatus for a printing press and, more particularly, to an ink fountain apparatus provided with a mechanism for adjusting the degree of opening of an ink supplying port by rotating an engaged screw to effect positional adjustment of an ink blade displaceable toward and away from a fountain roller.
2. Description of the Prior Art
For example, Japanese Utility Model Laid-Open No. 25329/1992 and Japanese Patent Laid-Open No. 84339/1990 disclose different prior arts of an ink fountain apparatus provided with a mechanism for adjusting the degree of opening of an ink supplying port, by rotating an engaged screw to effect positional adjustment of an ink blade displaceable toward and away from a fountain roller.
In the prior art disclosed in Japanese Utility Model Laid-Open No. 25329/1992, a gear for transmitting drive to the ink blade is engaged with a screw fixed at both ends thereof, and a stopper projection is provided so as to give the gear a reaction force acting in a direction opposite to the rotating direction of the gear. A stopper projection provided on one side of the gear is adapted to come into abutment with the aforesaid stopper projection, and the position in which the ink blade is stopped by the abutment defines the maximum or minimum limit of the degree of opening of the ink supplying port.
In the prior art disclosed in Japanese Patent Laid-Open No. 84339/1990, a potentiometer provided which interlocks with the gear for transmitting drive to the ink blade. When the potentiometer reaches a predetermined value, a driving motor is stopped so that the ink blade is stopped. The position of the ink blade at that time defines the maximum or minimum limit of the degree of opening of the ink supplying port.
The above-described prior art ink fountain apparatuses have the following disadvantages, respectively.
In the prior art disclosed in Japanese Utility Model Laid-Open No. 25329/1992, the abutment between the stopper projection for defining the maximum and minimum limits of the degree of opening of the ink supplying port and the stopper projection provided on one side of the driving transmitting gear is realized by utilizing the amounts of displacement of the side faces of the stopper projections due to one rotation of the gear, i.e., by using at most a thread portion of only one pitch of only the engaged screw.
As a result, because of the backlash of the thread of the screw, the position in which the ink blade is stopped by the stopper projections may be varied in the range of one rotation of the gear, i.e., the size of one pitch, or the ink blade may stop with the front end faces of the stopper projections butting against each other, so that accuracy will be impaired by the drawbacks. If the ink blade stops with the front end faces of the stopper projections butting against each other, the externally threaded portion of the gear and the screw may bite into each other ink the movement between them becomes stiff.
Further, adjustment of the attachment position of each of the stopper projections for the purpose of avoiding the above-described problems requires subtle and difficult processes, and the operation of assembling the stopper projections needs skill. This increases the burden of the workers.
In the prior art disclosed in Japanese Patent Laid-Open No. 84339/1990, since it is necessary to employ a potentiometer for detecting the maximum and minimum limits of the degree of opening of the ink supplying port, and an electrical circuit associated therewith, the cost increases and the accuracy is lowered by noise or the like.